Polymeric micelles as nanocarriers for drug delivery

Hyaluronic Acid within Self-Assembling Nanoparticles: Endless Possibilities for Targeted Cancer Therapy

Self-assembling nanoparticles (SANPs) based on hyaluronic acid (HA) represent unique tools in cancer therapy because they combine the HA targeting activity towards cancer cells with the advantageous features of the self-assembling nanosystems, i.e., chemical versatility and ease of preparation and scalability. This review describes the key outcomes arising from the combination of HA and SANPs, focusing on nanomaterials where HA and/or HA-derivatives are inserted within the self-assembling nanostructure. We elucidate the different HA derivatization strategies proposed for this scope, as well as the preparation methods used for the fabrication of the delivery device. After showing the biological results in the employed in vivo and in vitro models, we discussed the pros and cons of each nanosystem, opening a discussion on which approach represents the most promising strategy for further investigation and effective therapeutic protocol development.

Detection of Cerebrovascular Loss in the Normal Aging C57BL/6 Mouse Brain Using in vivo Contrast-Enhanced Magnetic Resonance Angiography

Microvascular rarefaction, or the decrease in vascular density, has been described in the cerebrovasculature of aging humans, rats, and, more recently, mice in the presence and absence of age-dependent diseases. Given the wide use of mice in modeling age-dependent human diseases of the cerebrovasculature, visualization, and quantification of the global murine cerebrovasculature is necessary for establishing the baseline changes that occur with aging. To provide in vivo whole-brain imaging of the cerebrovasculature in aging C57BL/6 mice longitudinally, contrast-enhanced magnetic resonance angiography (CE-MRA) was employed using a house-made gadolinium-bearing micellar blood pool agent. Enhancement in the vascular space permitted quantification of the detectable, or apparent, cerebral blood volume (aCBV), which was analyzed over 2 years of aging and compared to histological analysis of the cerebrovascular density. A significant loss in the aCBV was detected by CE-MRA over the aging period. Histological analysis via vessel-probing immunohistochemistry confirmed a significant loss in the cerebrovascular density over the same 2-year aging period, validating the CE-MRA findings. While these techniques use widely different methods of assessment and spatial resolutions, their comparable findings in detected vascular loss corroborate the growing body of literature describing vascular rarefaction aging. These findings suggest that such age-dependent changes can contribute to cerebrovascular and neurodegenerative diseases, which are modeled using wild-type and transgenic laboratory rodents.

Enhanced storage stability of solid lipid nanoparticles by surface modification of comb-shaped amphiphilic inulin derivatives

Solid lipid nanoparticles (SLNs) have been widely used as a vehicle for drug delivery. However, highly ordered lipid lattices and poor storage stability limit their practical application. Highly ordered crystal lattices may result from the low drug payload. In addition, the lipid matrix of SLNs may undergo a polymorphic transition from high energy and disordered modifications to low energy and ordered modifications during storage. This leads to drug expulsion and precipitation. Meanwhile, SLNs are susceptible to particle aggregation and size growth during storage. To improve the performance of SLNs, two comb-shaped amphiphilic macromolecular materials (CAMs), dodecyl inulin (Inu12) and octadecyl inulin (Inu18), were synthesized and utilized as emulsifiers to modify and stabilize SLNs (Inu12/Inu18-SLNs). The results indicated that Inu12 and Inu18 could more effectively reduce the lipid crystallinity and crystal lattice order of fresh SLNs versus Poloxamer 188 and Tween-80. Moreover, after six months of storage at 4 °C or 25 °C, both blank and Cyclosporine A (CsA)-loaded Inu12/Inu18-SLNs had a slower crystal transition than Tween/P188-SLNs. The particle size increases of Inu12/Inu18-SLNs were much smaller than those of Tween/P188-SLNs. The drug encapsulation efficiencies of CsA-loaded Inu12/Inu18-SLNs during storage decreased more slowly than Tween-SLNs. Therefore, Inu12 and Inu18 could more effectively inhibit lipid crystal transition and prevent particle aggregation during storage. This, in turn, leads to better storage physical stability of SLNs. Thus, the Inu12 and Inu18 CAMs were superior to Tween-80 and Poloxamer 188 (common straight-chain surfactants).

Bimetallic Zeolitic Imidazolate Framework as an Intrinsic Two-Photon Fluorescence and pH-Responsive MR Imaging Agent

Zeolitic imidazolate framework-8 (ZIF-8) has received wide attention in recent years as a potential drug vehicle for the treatment of cancer due to its acid-responsiveness and moderate biocompatibility. However, its congenital deficiency of intrinsic imaging capability limits its wider applications; therefore, a postsynthetic exchange approach was utilized to introduce paramagnetic manganese(II) ions into the ZIF-8 matrix. As a result, bimetallic zeolitic imidazolate frameworks (Mn-Zn-ZIF) were thus fabricated and exhibited pH-responsive T1-weighted magnetic resonance imaging (MRI) contrast effect. Remarkably, we also found its own fluorescence derived from 2-methylimidazole, which is the first report of the intrinsic two-photon fluorescence imaging of ZIFs to our knowledge. Mn-Zn-ZIF still preserves the original properties of ZIF-8 of high surface areas, microporosity, and acid sensitivity. After further PEGylation of Mn-Zn-ZIF, the nanoparticles showed no obvious toxicity and its MRI contrast effect has also been enhanced. Our work highlights the promise of modified zeolitic imidazolate frameworks as potential cancer theranostic platforms.

Topical Formulation of Self-Assembled Antiviral Prodrug Nanomicelles for Targeted Retinal Delivery

Topical drug administration for back of the eye delivery is extremely challenging due to the presence of protection mechanisms and physiological barriers. Self-assembled polymeric nanomicelles have emerged as promising vehicles for drug delivery. Apart from serving as an inert nanocarrier for therapeutic agents, polymeric nanomicelles are known to bypass mononuclear phagocytic system (MPS) and efflux transporters thereby improving drug bioavailability. In this investigation, a highly efficacious biotinylated lipid prodrug of cyclic cidofovir (B-C12-cCDF) was formulated within polymeric nanomicelles as a carrier for targeted retinal delivery. Polymeric nanomicelles were prepared from polyoxyethylene hydrogenated castor oil 40 (HCO-40) and octoxynol 40 (OC-40). In vitro release studies revealed that B-C12-cCDF-loaded nanomicelles released B-C12-cCDF at a faster rate in stimulated tear fluid (STF) in comparison to PBST. MTT and LDH assays demonstrated negligible cytotoxicity of B-C12-cCDF-loaded nanomicelles relative to CDF and B-C12-cCDF in HRPE (human retinal pigment epithelial, D407), HCE-T (human corneal epithelial), and CCL 20.2 (human conjunctival epithelial) cells. Confocal laser scanning microscopy and flow cytometry analyses indicated that B-C12-cCDF-loaded nanomicelles were efficiently internalized into D407 and HCE-T cells in contrast to CDF and B-C12-cCDF. Moreover, little B-C12-cCDF was also observed in the nuclei after 24 h of incubation. Polymeric nanomicelles carrying the transporter targeted prodrug did not produce any cytotoxic effects and were internalized into the cells effectively. Permeability experiments across HCE-T cells further confirmed significant transport of prodrug loaded nanomicelles and their subsequent uptake into D407 cells. These findings indicate that HCO-40/OC-40 based polymeric nanomicelles could become a promising topical delivery system for ocular administration of antiviral agents.

pH-sensitive micelles for targeted drug delivery prepared using a novel membrane contactor method

A novel membrane contactor method was used to produce size-controlled poly(ethylene glycol)-b-polycaprolactone (PEG-PCL) copolymer micelles composed of diblock copolymers with different average molecular weights, Mn (9200 or 10,400 Da) and hydrophilic fractions, f (0.67 or 0.59). By injecting 570 L m(-2) h(-1) of the organic phase (a 1 mg mL(-1) solution of PEG-PCL in tetrahydrofuran) through a microengineered nickel membrane with a hexagonal pore array and 200 μm pore spacing into deionized water agitated at 700 rpm, the micelle size linearly increased from 92 nm for a 5-μm pore size to 165 nm for a 40-μm pore size. The micelle size was finely tuned by the agitation rate, transmembrane flux and aqueous to organic phase ratio. An encapsulation efficiency of 89% and a drug loading of ~75% (w/w) were achieved when a hydrophobic drug (vitamin E) was entrapped within the micelles, as determined by ultracentrifugation method. The drug-loaded micelles had a mean size of 146 ± 7 nm, a polydispersity index of 0.09 ± 0.01, and a ζ potential of -19.5 ± 0.2 mV. When drug-loaded micelles where stored for 50 h, a pH sensitive drug release was achieved and a maximum amount of vitamin E (23%) was released at the pH of 1.9. When a pH-sensitive hydrazone bond was incorporated between PEG and PCL blocks, no significant change in micelle size was observed at the same micellization conditions.

Polymeric micelles and alternative nanonized delivery vehicles for poorly soluble drugs

Poorly soluble drugs often encounter low bioavailability and erratic absorption patterns in the clinical setting. Due to the rising number of compounds having solubility issues, finding ways to enhance the solubility of drugs is one of the major challenges in the pharmaceutical industry today. Polymeric micelles, which form upon self-assembly of amphiphilic macromolecules, can act as solubilizing agents for delivery of poorly soluble drugs. This manuscript examines the fundamentals of polymeric micelles through reviews of representative literature and demonstrates possible applications through recent examples of clinical trial developments. In particular, the potential of polymeric micelles for delivery of poorly water-soluble drugs, especially in the areas of oral delivery and in cancer therapy, is discussed. Key considerations in utilizing polymeric micelles' advantages and overcoming potential disadvantages have been highlighted. Lastly, other possible strategies related to particle size reduction for enhancing solubilization of poorly water-soluble drugs are introduced.

Theranostic implications of nanotechnology in multiple sclerosis: a future perspective

Multiple Sclerosis is a multifactorial disease with several pathogenic mechanisms and pathways. Successful MS management and medical care requires early accurate diagnosis along with specific treatment protocols based upon multifunctional nanotechnology approach. This paper highlights advances in nanotechnology that have enabled the clinician to target the brain and CNS in patient with multiple sclerosis with nanoparticles having therapeutic and imaging components. The multipartite theranostic (thera(py) + (diag)nostics) approach puts forth strong implications for medical care and cure in MS. The current nanotheranostics utilize tamed drug vehicles and contain cargo, targeting ligands, and imaging labels for delivery to specific tissues, cells, or subcellular components. A brief overview of nonsurgical nanorepair advances as future perspective is also described. Considering the potential inflammatory triggers in MS pathogenesis, a multifunctional nanotechnology approach will be needed for the prognosis.

A review on comb-shaped amphiphilic polymers for hydrophobic drug solubilization

Comb-shaped amphiphilic polymers are rapidly emerging as an alternative approach to amphiphilic block copolymers for hydrophobic drug solubilization. These polymers consist of a homopolymer or copolymer backbone to which hydrophobic and hydrophilic pendant groups can be grafted resulting in a comb-like architecture. The hydrophobic pendants may consist of homopolymers, copolymers and other low-molecular weight hydrophobic structures. In this review, we focus on hydrophobically modified preformed homopolymers. Comb-shaped amphiphilic polymers possess reduced critical aggregation concentration values compared with traditional surfactant micelles indicating increased stability with decreased disruption experienced on dilution. They have been fabricated with diverse architectures and multifunctional properties such as site-specific targeting and external stimuli-responsive nature. The application of comb-shaped amphiphilic polymers is expanding; here we report on the progress achieved so far in hydrophobic drug solubilization for both intravenous and oral delivery.

Enhancement of cellular uptake and antitumor efficiencies of micelles with phosphorylcholine

Internalization of drug delivery micelles into cancer cells is a crucial step for antitumor therapeutics. Novel amphiphilic star-shaped copolymers with zwitterionic phosphorylcholine (PC) block, 6-arm star poly(ε-caprolactone)-b-poly(2-methacryloyloxyethyl phosphorylcholine) (6sPCL-b-PMPC), have been developed for encapsulation of poorly water-soluble drugs and enhancement of their cellular uptake. The star-shaped copolymers were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The copolymers self-assembled to form spherical micelles with low critical micelle concentration (CMC). The sizes of the micelles range from 80 to 170 nm and increase 30 ≈ 80% after paclitaxel (PTX) loading. Labeled with fluorescein isothiocyanate (FITC), the micelles were confirmed by fluorescence microscopy to have been internalized efficiently by tumor cells. Direct visualization of the micelles within tumor cells by transmission electron microscopy (TEM) confirmed that the 6sPCL-b-PMPC micelles were more efficiently uptaken by tumor cells compared to PCL-b-PEG micelles. When incorporated with PTX, the 6sPCL-b-PMPC micelles show much higher cytotoxicity against Hela cells than PCL-b-PEG micelles, in response to the higher efficiency of cellular uptake.

In vitro and in vivo anticancer activity of a novel nano-sized formulation based on self-assembling polymers against pancreatic cancer

PURPOSE

To evaluate the in vitro and in vivo pancreatic anticancer activity of a nano-sized formulation based on novel polyallylamine grafted with 5% mole cholesteryl pendant groups (CH(5)-PAA).

METHODS

Insoluble novel anticancer drug, Bisnaphthalimidopropyldiaaminooctane (BNIPDaoct), was loaded into CH(5)-PAA polymeric self-assemblies by probe sonication. Hydrodynamic diameters and polydispersity index measurements were determined by photon correlation spectroscopy. The in vitro cytotoxicity evaluation of the formulation was carried out by the sulforhodamine B dye assay with human pancreatic adenocarcinoma BxPC-3 cells, while for the in vivo study, Xenograff mice were used. In vitro apoptotic cell death from the drug formulation was confirmed by flow cytometric analysis.

RESULTS

The aqueous polymer-drug formulation had a mean hydrodynamic size of 183 nm. The drug aqueous solubility was increased from negligible concentration to 0.3 mg mL(-1). CH(5)-PAA polymer alone did not exhibit cytotoxicity, but the new polymer-drug formulation showed potent in vitro and in vivo anticancer activity. The mode of cell death in the in vitro study was confirmed to be apoptotic. The in vivo results revealed that the CH(5)-PAA alone did not have any anti-proliferative effect, but the CH(5)-PAA-drug formulation exhibited similar tumour reduction efficacy as the commercial drug, gemcitabine.

CONCLUSIONS

The proposed formulation shows potential as pancreatic cancer therapeutics.

Biological evaluation of polymeric micelles with covalently bound doxorubicin

The main limitation of contemporary anticancer chemotherapy remains to be the insufficient specificity of the drugs for tumor tissue, which decreases the maximum tolerated dose due to severe side effects. Micellar drug delivery systems based on amphiphilic block copolymers with a very narrow size distribution (10 to 100 nm in diameter) is a novel innovative approach. Here, we report biological and pharmacological properties of polymeric micellar conjugate containing doxorubicin (DOX) covalently bound via hydrolytically cleavable hydrazone bonds to the micelle core. The system had a very low systemic toxicity (almost 20 times lower than free DOX) and long circulation in the bloodstream (with half of the dose after 24 h). Significant accumulation of tested micelles within the tumor was confirmed by fluorescent whole body imaging. Our new micellar system showed promising therapeutic activity against established murine EL-4 T-cell lymphoma; it was found that it is able to completely cure about 75% of tumor-bearing mice (with doses of either 1 x 150 mg DOX kg(-1) or 2 x 75 mg DOX kg(-1), administered i.v.). Moreover, treatment with micelles in cured mice induced tumor-specific resistance. Up to 80% of these mice survived rechallenge with original but not with distinct tumor cells.

Gold nanoparticles stabilized by thermosensitive diblock copolymers of poly(ethylene glycol) and polyphosphoester

Aqueous dispersions of thermosensitive gold nanoparticles protected by diblock copolymers of poly(ethylene glycol) and polyphosphoester were prepared and studied. Diblock copolymers MPEG-b-P(EEP-co-PEP) with different compositions that are composed of monomethoxy poly(ethylene glycol), random copolymer of ethyl ethylene phosphate (EEP), and isopropyl ethylene phosphate (PEP) were synthesized by ring-opening polymerization in bulk. Thioctic acid was then conjugated to the terminal hydroxyl group of the polyphosphoester block by esterification. Gold nanoparticles were then prepared by a one-step method and showed core-shell structure with an average gold core diameter of about 10 nm surrounded by a MPEG-b-P(EEP-co-PEP) shell with a thickness of about 30 nm. These polymer stabilized gold nanoparticles are reversibly thermosensitive in aqueous medium, exhibiting tunable collapse temperatures which are dependent on the composition of the diblock copolymers. Methyl tetrazolium (MTT) assay against HEK 293 cells demonstrated that these gold nanoparticles are with good biocompatibility. These gold nanoparticles protected by thermosensitive diblock copolymers with tunable collapse temperature are expected to be useful for biomedical applications.

Block copolymer micelles as nanocontainers for controlled release of proteins from biocompatible oil phases

Biocompatible oils are used in a variety of medical applications ranging from vaccine adjuvants to vehicles for oral drug delivery. To enable such nonpolar organic phases to serve as reservoirs for delivery of hydrophilic compounds, we explored the ability of block copolymer micelles in organic solvents to sequester proteins for sustained release across an oil-water interface. Self-assembly of the block copolymer, poly(-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP), was investigated in toluene and oleic acid, a biocompatible naturally occurring fatty acid. Micelle formation in toluene was characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM) imaging of micelles cast onto silicon substrates. Cryogenic transmission electron microscopy confirmed a spherical morphology in oleic acid. Studies of homopolymer solubility implied that micelles in oleic acid consist of a P2VP corona and a PCL core, while P2VP formed the core of micelles assembled in toluene. The loading of two model proteins (ovalbumin (ova) and bovine serum albumin (BSA)) into micelles was demonstrated with loadings as high as 7.8% wt of protein per wt of P2VP in oleic acid. Characterization of block copolymer morphology in the two solvents after protein loading revealed spherical particles with similar size distributions to the as-assembled micelles. Release of ova from micelles in oleic acid was sustained for 12-30 h upon placing the oil phase in contact with an aqueous bath. Unique to the situation of micelle assembly in an oily phase, the data suggest protein is sequestered in the P2VP corona block of PCL-b-P2VP micelles in oleic acid. More conventionally, protein loading occurs in the P2VP core of micelles assembled in toluene.

Self-assembling materials for therapeutic delivery

A growing number of medications must be administered through parenteral delivery, i.e., intravenous, intramuscular, or subcutaneous injection, to ensure effectiveness of the therapeutic. For some therapeutics, the use of delivery vehicles in conjunction with this delivery mechanism can improve drug efficacy and patient compliance. Macromolecular self-assembly has been exploited recently to engineer materials for the encapsulation and controlled delivery of therapeutics. Self-assembled materials offer the advantages of conventional crosslinked materials normally used for release, but also provide the ability to tailor specific bulk material properties, such as release profiles, at the molecular level via monomer design. As a result, the design of materials from the "bottom up" approach has generated a variety of supramolecular devices for biomedical applications. This review provides an overview of self-assembling molecules, their resultant structures, and their use in therapeutic delivery. It highlights the current progress in the design of polymer- and peptide-based self-assembled materials.